Rotary actuator for disk drive

ABSTRACT

Described herein is a moving coil type rotary actuator for a disk drive, which essentially includes: a rotary arm supporting transducer means at one end thereof, and rotatably supported for rotation about an axis; a first york arranged in a first plane perpendicular to the rotational axis; a second york arranged in a second plane in a spaced relation parallel with the first york and perpendicular to the rotational axis; a first permanent magnet mounted on the surface of the first york to produce a first magnetic field between the second york and itself; a second permanent magnet mounted on one surface of the second york in staggered relation with the first magnet on the first york to produce a second magnetic field between the first york and itself; and a moving coil supported by the rotary arm at the other end thereof and having first and second coil portions positioned within the first and second magnetic fields, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetic disk drive such as a hard diskdrive or the like, and more particularly to a moving coil type rotaryactuator suitable for used on a magnetic disk drive for driving amagnetic head arm in accessing to a specified track on a disk.

2. Description of the Prior Art

In a magnetic disk drive, in order to gain access to a specified trackon a disk, a magnetic head arm is driven by a moving coil type rotaryactuator which is arranged, for example, as shown in FIG. 1. Fortracking a specific track by a magnetic head 51 on one end of a magnetichead arm 52, a moving coil 53 is provided at the other end of the armwhich is rotatably supported on a rotational shaft 54.

Located on the opposite sides of the moving coil 53 are first and secondyorks 55 and 56 which have first and second pairs of permanent magnets57 and 58 and 59 and 60 (each pair being formed by the adjacentlypositioned magnets) securely fixed thereon. The moving coil 53 isrotatably supported between the inner opposing surfaces of the first andsecond yorks 55 and 56 with the first and second pairs of permanentmagnets 57 and 58 and 59 and 60, respectively.

As shown in FIG. 2, the moving coil 53 is constituted by first andsecond effective coil portions 61 and 62, first and second ineffectivecoil portions 63 and 64, and R (round) portions 65 to 68 connecting thefirst and second effective coil portions 61 and 62 with the first andsecond ineffective coil portions 63 and 64.

The first and second pairs of permanent magnets 57 and 58 and 59 and 60are each arranged to have an inverse polarity on the side of the firstand second effective coil portions 61 and 62 (or on the side of themagnetic gap) relative to the other one of the same pair (the magnetsfixed on the same yoke) and relative to the opposing one of the otherpair (the magnets fixed on the other yoke) as shown in FIG. 3. Namely,for example, facing the effective coil portions 61 and 62, the permanentmagnet 57 has the N pole, the permanent magnet 58 the S pole, thepermanent magnet 59 the S pole, and the permanent magnet 60 the N pole.

In operation of the prior art moving coil actuator of theabove-described arrangement, if current I is passed through theeffective coil portions 61 and 62 of the moving coil 53 in the directionshown in FIG. 3, a propulsive force urges the moving coil 53 in thedirection of arrow A according to Flemming's left-hand rule, turning thearm 52 and the magnetic head 51 for access to a specified track.Conduction of current I in the opposite direction generates a propulsiveforce in the opposite direction.

Recently, the moving coil type actuators for magnetic disk drives havebeen required to have a greater propulsive force in order to meet thestrong demands for reductions in size and thickness. In this connection,magnets of rare earth cobalt, like samarium, with a large energyproduct, are resorted to as permanent magnets in most cases. However,since rare earth cobalt magnets are very expensive, attempts have beenmade to enhance the efficiency in usage of such permanent magnets,reducing the weights of the permanent magnets by eliminating them fromthose portions which do not effectively contribute to generation of thepropulsive force. The first and second effective coil portions 61 and 62contribute to the propulsive force while the first and secondineffective coil portions 63 and 64 do not. The R portions 65 to 68contribute to the propulsive force only at a rate smaller than 50% interms of their length, and obviously not at a rate of 100%. Therefore,it is often the case to employ an arrangement in which the first andsecond pairs of permanent magnets 57 and 58 and 59 and 60 have widthswhich are equal to the length of the effective coil portions 61 and 62in width in a direction perpendicular to the direction of the propulsiveforce on the moving coil 53.

FIG. 4 illustrates another prior art moving coil type rotary actuatorwhich has only the second pair of permanent magnets 59 and 60 fixed onthe second yoke 56.

In case of the conventional moving coil type rotary actuators as shownin FIGS. 1 through 4, which have the first pair of permanent magnets 57and 58 and/or the second pair of permanent magnets 59 and 60 fixed sideby side on the first yoke 55 and/or the second yoke 56 in such a manneras to have inverse polarity relative to the other one, there arises aproblem of diminution of main flux φ_(M) due to leakage flux φ_(R) ofminor loop as shown in FIG. 3.

Consequently, the propulsive force of the actuator becomes weaker,resulting in a slower access to a desired track. Therefore, it becomesnecessary to provide larger permanent magnets to compensate for thediminution of the main flux φ_(M), which makes it difficult to reducethe size of the actuator as a whole and, due to expensiveness of themagnets, invites a substantial increase in cost.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention contemplates a solution to the above-mentionedproblems of the prior art, and has as its object the provision of amoving coil type rotary actuator with improved propulsive force, whichis arranged to reduce the leakage flux between the first and secondpermanent magnets to prevent diminution of the main flux.

In accordance with the present invention, there is provided a rotaryactuator for a disk drive, which essentially comprises: a rotary armsupporting transducer means at one end thereof, and rotatably supportedfor rotation about an axis; a first yoke arranged in a first planeperpendicular to the rotational axis; a second yoke arranged in a secondplane in a spaced relation parallel with the first yoke andperpendicularly to the rotational axis; a first permanent magnet mountedon one surface of the first yoke to produce a first magnetic fieldbetween the second yoke and itself; a second permanent magnet mounted onone surface of the second yoke in staggered relation with the firstmagnet on the first yoke to produce a second magnetic field between thefirst yoke and itself; and a moving coil supported by the rotary arm atthe other end thereof and having first and second coil portionspositioned within the first and second magnetic fields, respectively.

According to an aspect of the invention, the moving coil is formed in astepped form holding the first coil portion closer to the second yokethan to the first yoke while holding the second coil portion closer tothe first yoke than to the second yoke.

The above and other objects, features and advantages of the inventionwill become apparent from the following description and the appendedclaims, taken in conjunction with the accompanying drawings which showby way of example a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a disassembled perspective view of a conventional moving coiltype actuator;

FIG. 2 is a plan view of the moving coil of the conventional actuator;

FIG. 3 is a sectional view of major components of the conventionalactuator;

FIG. 4 is a disassembled perspective view of another conventional movingcoil type actuator;

FIG. 5 is a disassembled perspective view of a moving coil type actuatoraccording to the invention;

FIG. 6 is a plan view of the moving coil of the actuator according tothe invention; and

FIG. 7 is a sectional view of major components of the actuator accordingto the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 5, there is shown a moving coil type actuatorembodying the present invention, in which, for accessing a specifiedtrack on a magnetic disk, a magnetic head 1 is mounted on one end of amagnetic head arm 2 which supports a moving coil 3 at the other endthereof and which is rotatably supported by a rotational shaft 4.

The actuator further includes first and second permanent magnets 7 and 8which are securely fixed on opposing surfaces of parallel first andsecond yokes 5 and 6, respectively, in staggered positions or innon-overlapping relation with each other. The yokes 5 and 6 are each inthe form of a thin flat strip which can be fabricated at low cost. Onthe other hand, the first and second permanent magnets 7 and 8 aremagnets of rare earth cobalt like samarium, which has a large energyproduct. The moving coil 3 is rotatably supported between and in aface-to-face relationship with the first and second yokes 5 and 6 andwith the first and second permanent magnets 7 and 8.

The moving coil 3 is formed by winding conductive wire and, as shownparticularly in FIGS. 5 and 7, has a stepped shape. Further, as shown inFIG. 6, the moving coil 3 is comprised of first and second effectivecoil portions 9 and 10, first and second ineffective coil portions 11and 12, and R (round) portions 13 to 16 connecting the first and secondeffective coil portions 9 and 10 with the first and second ineffectivecoil portions 11 and 12.

In a direction perpendicular to the propulsive force on the moving coil3, the first and second permanent magnets 7 and 8 are dimensioned tohave a width slightly smaller than the length of the first and secondeffective coil portions 9 and 10. Arrangements are made to keep thefirst and second permament magnets 7 and 8 from contacting the first andsecond ineffective coil portions 11 and 12.

Specifically, as shown particularly in FIG. 7, the moving coil typeactuator of the invention is arranged such that the first effective coilportion 9 of the moving coil 3 faces on one side thereof the firstpermanent magnet 7 through a magnetic gap and on the other side facesthe second yoke 6 directly through a magnetic gap. The second effectivecoil portion 10 is arranged to face on one side thereof the first yoke 5directly through a magnetic gap and on the other side to face the secondpermanent magnets 8 through a magnetic gap.

The first and second permanent magnets 7 and 8 are arranged to have thesame polarity, for example, the north pole on the inner side which facesthe first or second effective coil portion 9 or 10 (or on the side whichfaces the magnetic gap).

In operation, upon passing current I through the first and secondeffective coil portions 9 and 10 of the moving coil 3 in the directionshown in the drawing, a propulsive force urges to the moving coil 3 inthe direction of arrow A according to Flemming's left-hand rule, turningthe arm 2 and the magnetic head 1 on the arm for access to a specifiedtrack on a disk. A propulsive force of the opposite direction isgenerated by reversing the current direction.

It will be appreciated from the foregoing description that, with thearrangements according to the invention, the thickness of the actuatoras a whole is determined by the first and second yokes, one of the firstand second permanent magnets and the magnetic gaps, so that it can bemade thinner as compared with its conventional counterpart, in a degreecorresponding to the thickness of one permanent magnet. While retainingthe functions of the conventional counterparts, a significant reductionin cost is made possible by the arrangement of the invention,eliminating expensive rare earth cobalt magnets from those portionswhich do not effectively contribute to the propulsive force and by usingflat, strip-like yokes. In addition, the first and second permanentmagnets are fixed in staggered positions on the yokes and arranged tohave the same pole on the side of the magnetic gap, so that it becomespossible to reduce the leakage flux between the two permanent magnets,preventing diminution of the main flux to guarantee an improvedpropulsive force.

What is claimed is:
 1. A rotary actuator for a disk drive, comprising:arotary arm supporting transducer means at one end thereof, and rotatablysupported for rotation about an axis; a first yoke arranged in a firstplane perpendicular to said rotational axis; a second yoke arranged in asecond plane in parallelly spaced relation parallel with said first yokeand perpendicular to said rotational axis; a first permanent magnetmounted on one surface of said first yoke to produce a first magneticfield between said second yoke and itself; a second permanent magnetmounted on one surface of said second yoke in staggered relation withsaid first magnet to produce a second magnetic field between said firstyoke and itself; and a moving coil supported by said rotary arm at theother end thereof and having first and second effective coil portionspositioned within said first and second magnetic fields, respectively.2. A rotary actuator for a disk drive according to claim 1, wherein saidmoving coil is formed in a stepped shape holding said first coil portioncloser to said second yoke than to said first yoke while holding saidsecond portion closer to said first yoke than to said second yoke.
 3. Arotary actuator for a disk drive according to claim 1, wherein saidfirst and second magnets are made of rare earth cobalt includingsamarium.
 4. A rotary actuator for a disk drive according to claim 1,wherein said first and second permanent magnets are arranged to have thesame polarity on the side of said magnetic gap.
 5. A rotary actuator fora disk drive according to claims 1 to anyone of 4, wherein said firstand second yokes are each in the form of a thin flat strip.